1. Field of the Invention
The invention relates to window balances, more specifically to preloading of a window balance that comprises a torsion spring and a tension spring.
2. Description of the Prior Art
U.S. Pat. No. 5,152,032 patented Oct. 6, 1992 by Davis et al. describes a tension plus torsion balance. In this tension plus torsion balance the torsion spring is turned at one end of the spring by a follower. The follower is rotated by a spiral rod that is threadably engaged with the follower so that moving the spiral rod longitudinally through the follower rotates the follower. The spiral rod is moved longitudinally by a window sash as the sash is lifted and lowered, by a first eyelet at one end of the rod that is attached to the window sash.
In order to provide a predetermined baseline lifting force to be transmitted back to the sash, the torsion spring is preloaded by gripping a second eyelet adjacent to the first eyelet when the first eyelet is not attached to the sash, and twisting the rod until the desired force is obtained, then while holding the rod at that rotational position, attaching the rod to the sash by the first eyelet. U.S. Pat. No. 5,152,032 is hereby incorporated by reference.
In M. H. Gregg et al. , U.S. Pat. No. 2,890,480 patented Jun. 16, 1959 the sash is lifted and the preload adjustment is made by moving a first driver of a dog-tooth clutch that is in axial alignment with the spiral rod, past a lock pin and into the second driver of the dog tooth that is attached to the end of the spiral rod, and turning the first driver.
In Larson et al., U.S. Pat. No. 2,825,089 patented Mar. 4, 1958 a slotted head for a screw driver is mounted in axial alignment on the end of the spiral rod. The head is journaled in a laterally oriented slot, pulled to one end of the slot against a ratchet pawl by a convolute spring. Increase in minimum lifting force is made by turning the screw as the pawl enters successive notches around the head. Decrease in minimum lifting force is made by moving the head laterally in the slot against the urging of the convolute spring until the notched periphery of the screw head is drawn away from the paw, and reversing the direction of the screw.